Method for operating an electric drive system, computer program product, data carrier, electric drive system and motor vehicle

Abstract

The invention relates to a method for operating an electric drive system (1), in particular for a motor vehicle, the electric drive system (1) having a set of power electronics (2), in particular an electrical voltage transformer, an electric machine (3) that is controllable by the set of power electronics (2), and a battery (4) that is electrically connected or connectable to the set of power electronics (2), and wherein the set of power electronics (2) has at least one electrical phase (5) for controlling the electric machine (3). In said method, at least one voltage value of an electrical DC-link voltage (U1) of the set of power electronics (2) is estimated using a mathematical model of the drive system (1) as a function of a specified rotational speed and / or torque demand on the electric machine (3), at least one current value of an electrical current for one of the phases (5) and / or a rotor of the electric machine (3) is specified as a function of the rotational speed and / or torque demand on the electric machine (3) and the estimated intermediate circuit voltage (U1), and the electric machine (3) is controlled on the basis of the specified current value.

Description

[0001] Description

[0002] title

[0003] Method for operating an electric drive system, computer program product, data carrier, electric drive system, motor vehicle

[0004] The invention relates to a method for operating an electric drive system, in particular for a motor vehicle, wherein the electric drive system has power electronics, in particular an electrical voltage converter, an electrical machine that can be controlled by the power electronics, and a battery that is or can be electrically connected to the power electronics, and wherein the power electronics has at least one electrical phase for controlling the electrical machine.

[0005] Furthermore, the invention relates to a computer program product that performs the above-mentioned method when the computer program product is executed on a computer device. Furthermore, the invention relates to a data storage medium comprising such a computer program product and an electric drive system comprising the computer device, which is specifically configured to execute the computer program product or the above-mentioned method. Finally, the invention relates to a motor vehicle comprising the electric drive system.

[0006] State of the art

[0007] Methods, electric drive systems, and motor vehicles of the type mentioned above are known from the prior art. For example, in electrical machines designed as separately excited synchronous machines, which are used for traction drives in battery-electric vehicles, a rotor flux and thus an induced rotor voltage are typically adjusted via an excitation current. This excitation current control is typically implemented highly dynamically, in particular with a fast two-point controller or a fast PI controller. Because the inductance of the rotor of the electrical machine is usually very high, a change in the stator currents is only possible comparatively slowly despite the highly dynamic control.

[0008] Corresponding efficiency-optimized current setpoints for the stator currents in the d- and q-direction of the field-oriented control and for a rotor current are stored, for example, as tables. These values ​​are typically specified for a field-oriented control and a rotor current control, with these setpoints being adjusted as dynamically and precisely as possible by the corresponding controls. For efficiency reasons, for example, in traction drives for battery-electric vehicles, an efficiency-optimized and thus low rotor current is set for low torque requirements. If a high torque is required quickly, the necessary rotor current can only be provided after a certain period of time, as described above.Therefore, a rise limiter is used in particular for the current setpoints for the stator currents, so that the necessary rotor current is built up first and then the appropriate stator currents, because without rotor current the stator currents cannot set a sufficient torque.

[0009] In order to control the electric machine with the associated power electronics for maximum efficiency, the required stator currents must be set with the lowest possible DC link voltage. For example, the electric machine and power electronics are designed such that they can still provide the required torque at the lowest DC link voltage encountered. Accordingly, the characteristic maps of the current setpoints for the field-oriented control are calculated for precisely this lowest DC link voltage. As long as the electric machine and power electronics are operated on a stationary power grid or are supplied with power from it, the DC link voltage is comparatively stable, so it is sufficient to use only characteristic maps for a constant DC link voltage.If, however, the electric machine and the power electronics are operated on a mobile energy storage device, i.e. a battery or an accumulator, or are supplied with power from this, as provided in the method according to the invention, significantly greater fluctuations in the intermediate circuit voltage are to be expected, depending on the state of the energy storage device.

[0010] For example, the control system and the characteristic maps for the current setpoints are set to the lowest occurring DC link voltage to ensure that sufficient control reserves are available and the control behavior leads to advantageous current control. When a motor torque is set, the battery is loaded, and the DC link voltage drops significantly. For this purpose, the lowest occurring DC link voltage, i.e. the largest drop in the DC link voltage, is usually assumed for a "worst-case" battery condition, where the battery is, for example, maximally discharged, has a minimum temperature, and is at an advanced or maximum state of aging. Furthermore, a maximum electrical draw of all auxiliary consumers and the drive is usually assumed.

[0011] Disclosure of the invention

[0012] The method according to the invention with the features of claim 1 is characterized in that at least one voltage value of an electrical intermediate circuit voltage of the power electronics is estimated with the aid of a mathematical model of the drive system as a function of a predetermined speed and / or torque requirement for the electrical machine, that at least one current value of an electrical current for one of the phases and / or a rotor of the electrical machine is predetermined as a function of the speed and / or torque requirement for the electrical machine and of the estimated intermediate circuit voltage, and that the electrical machine is controlled as a function of the predetermined current value.Typically, when controlling an electric machine, as described above, an excitation current is specified, for example to set a specific torque for the electric machine, particularly at a specified speed of the electric machine. This excitation current is selected from a characteristic map as a function of a minimum available intermediate circuit voltage (voltage collapses under load), whereby a "worst-case scenario" (state of the battery and drive system) is usually assumed. By appropriately estimating the intermediate circuit voltage and taking the estimated intermediate circuit voltage into account when specifying the current value, it is advantageously ensured that the electric machine is operated with a further improved electrical efficiency or is controlled by the power electronics.Particularly preferably, current values ​​are specified for the excitation current and stator currents. The method according to the invention increases the efficiency of the control because the actual or estimated intermediate circuit voltage is usually higher than the minimum intermediate circuit voltage occurring when the torque is reached, for example because the battery is fully charged or only partially discharged, new or warm, and thus the intermediate circuit voltage drops significantly less than assumed under load. The method according to the invention estimates the actually expected (higher) intermediate circuit voltage and, in particular, selects a suitable characteristic map with a higher intermediate circuit voltage for the control, thus optimizing the control. The core of the method is the optimization of the corresponding control and regulation concept.In particular, the voltage value of the intermediate circuit voltage is estimated using the mathematical model of the drive system, assuming a known speed for a given torque setpoint. The mathematical model takes into account, in particular, at least one battery parameter, a power value of the electrical consumption of the electric drive system, and / or an efficiency of the electric machine and power electronics, particularly as a function of the speed and / or torque requirement. The speed depends, in particular, on the driving speed of the motor vehicle, provided the electric drive system is used in a motor vehicle.The torque setpoint is determined in particular by a corresponding control level, for example a control device, and / or depending on a corresponding request from a user of the electric drive system, in particular an acceleration request from the driver of the motor vehicle. The current values, in particular the stator currents and the rotor current, as described above, are set for the torque setpoint at a current speed using a stationary intermediate circuit voltage of the power electronics. Rather than initially setting current values ​​as a function of an assumed excessively low intermediate circuit voltage, which are then corrected, for example, when the torque setpoint is reached, the method according to the invention already sets the current values ​​correctly in a stationary manner to suit the expected, i.e. estimated, intermediate circuit voltage.Corresponding iteration steps for correcting the current values, as described above, are advantageously eliminated with the method according to the invention. For this immediate, correct adjustment of the current values, the mathematical model of the drive system is required. The advantage of the method is that the intermediate circuit voltage expected at the torque setpoint and the speed is at least approximately estimated in advance using the model, and optimal characteristic maps or controller parameters are selected virtually instantaneously. This improves the dynamics and efficiency of the drive system, as described above. No additional hardware is required; only a corresponding control system and a corresponding mathematical model for the intermediate circuit voltage.

[0013] According to a preferred development of the invention, the mathematical model takes into account a resistance value of the internal resistance of the battery and / or a voltage value of the battery's open-circuit voltage. By taking the resistance value and / or the voltage value into account, it is advantageously ensured that a load and / or wear state of the battery is represented in the mathematical model.

[0014] Particularly preferably, it is provided that the resistance value and / or the voltage value are determined as a function of a battery temperature and / or an age of the battery. By determining the resistance value and / or the voltage value in this way, a particularly simple possibility for their determination is created. Particularly preferably, the resistance value and / or the voltage value are adapted by a battery management system executed on a control device assigned to the battery based on the temperature and aging of the battery. Because the temperature changes relatively slowly and aging is very sluggish, the temperature and aging values ​​are alternatively transmitted to a further control device, in particular a computer device, which carries out the method according to the invention, for example via an already existing vehicle bus, in order to adapt the resistance value and / or the voltage values ​​there.

[0015] According to a preferred development of the invention, the mathematical model takes into account a power value of the electrical consumption of an electrical consumer connected to the battery. Taking the electrical consumption into account in this way advantageously ensures that the mathematical model is more closely approximated to the actual load situation of the electric drive system.

[0016] Particularly preferably, the mathematical model takes into account a power value of the electric drive power of the drive system. Taking the electric drive power into account in this way results in the advantage that the mathematical model is more closely approximated to the actual load situation of the electric drive system.

[0017] According to a preferred development of the invention, the current value for the specified speed or torque requirement is retrieved from a characteristic map associated with the estimated voltage value of the intermediate circuit voltage, in particular a look-up table. Using such a characteristic map provides a particularly simple and reliable way of retrieving the current value.

[0018] Particularly preferably, the mathematical model is designed as an observer, wherein the estimated voltage value for the intermediate circuit voltage is compared with a measured voltage value. This results in the advantage that the accuracy of the estimate of the intermediate circuit voltage is further improved. After comparing the voltage values, the states are, in particular, adapted. When using an extended Kalman filter, its parameters are particularly preferably also adapted. Further preferably, the adaptation or correction of the states or parameters is suspended when the model is used to estimate the intermediate circuit voltage for a desired torque to be applied in the future.

[0019] The computer program product according to the invention for execution on a computer device having the features of claim 8 is characterized in that, when used as intended, it executes the method according to the invention. This results in the advantages already mentioned.

[0020] The data carrier according to the invention with the features of claim 9 is characterized by the computer program product according to the invention stored thereon.

[0021] The electric drive system, in particular for a motor vehicle, with the features of claim 10 has power electronics, in particular an electrical voltage converter, an electric machine controllable by the power electronics, and a battery electrically connected or connectable to the power electronics, wherein the power electronics has at least one electrical phase for controlling the electric machine. The electric drive system is characterized by a computer device that is specifically designed to carry out the method according to the invention or to execute the computer program product according to the invention. This also results in the advantages already mentioned above. Preferably, the computer device is a control unit assigned to the electric drive system, in particular arranged in the motor vehicle. The electric machine is in particular a separately excited synchronous machine, as described above.Alternatively, the electric machine is another separately excited machine controlled by power electronics, a permanent magnet or electrically excited synchronous machine, or an asynchronous machine. The electric drive system is intended in particular for use in an industrial machine or a household appliance, especially white goods.

[0022] The motor vehicle with the features of claim 11 is characterized by the electric drive system according to the invention. This also results in the aforementioned advantages.

[0023] Further preferred features and combinations of features emerge from the above description and from the claims. The invention is explained in more detail below with reference to the drawings.

[0024] Figure 1 is a schematic representation of an electric drive system,

[0025] Figure 2 shows a first electrical equivalent circuit diagram for a mathematical model of the drive system,

[0026] Figure 3 shows a second electrical equivalent circuit for the model, and

[0027] Figure 4 shows a method for operating the drive system.

[0028] Figure 1 shows a schematic representation of an electric drive system 1. The electric drive system 1 has a power electronics unit 2, in this case an electrical voltage converter, in particular an inverter, an electrical machine 3 that can be controlled by the power electronics unit 2 and a battery 4 that is electrically connected to the power electronics unit 2.

[0029] The power electronics 2 are designed to control at least one electrical phase 5, in this case all three electrical phases 5, of the electrical machine 3. For this purpose, the power electronics 2 is assigned to a computer device 6, in particular a control device.

[0030] Figure 2 shows a first electrical equivalent circuit diagram for a mathematical model of the electric drive system 1. Using this model, it is possible to estimate an intermediate circuit voltage Ui of the power electronics 2. The equivalent circuit diagram includes electrical switching elements that model the parameters of the battery 4, as well as the electrical auxiliary loads and the drive itself.

[0031] The electrical equivalent circuit is derived from equivalent circuits known from the technical literature. The parameters of battery 4 are represented by two electrical resistors Ri, R2, each connected in parallel with capacitors Ci, C2, thus forming RC elements. A further resistor Ro and an inductor Lo are arranged in series.

[0032] These components together represent relevant parameters of battery 4. Battery 4 has an open-circuit voltage Uo and an output voltage U2. For example, an auxiliary load characterized by an electrical power P3, an electrical current I3, and an electrical voltage U3 is connected to battery 4.

[0033] Finally, the power electronics 2 are connected to the battery 4, wherein further losses, in particular line losses in a wiring, for example an on-board network, between the battery 4 and the power electronics 2, are represented by a further resistor R4 and an inductance L4.

[0034] The corresponding intermediate circuit voltage Ui, an intermediate circuit current h and an intermediate circuit power Pi then result at the power electronics 2. Knowing the values ​​of the corresponding electrical components, these can be estimated using the model.

[0035] However, for calculating the intermediate circuit voltage Ui for control purposes, the steady-state intermediate circuit voltage is primarily relevant. A simplified equivalent circuit diagram is sufficient to calculate this. This is shown as a second electrical equivalent circuit diagram for the model in Figure 3.

[0036] Instead of the aforementioned battery parameters from Figure 2, only a single resistor R5 is shown, which represents the overall internal resistance of the battery. To estimate the intermediate circuit voltage Ui, the open-circuit voltage Uo and the internal resistance R5 are sufficient as parameters of battery 4. The losses between and in the wiring and power electronics 2 are represented only by the resistor R4. The other electrical components are omitted.

[0037] Finally, an advantageous method for operating the electric drive system 1 will be described with reference to Figure 4. Figure 4 shows the method using a flowchart. In particular, the method ensures that the electric machine 3 is operated and controlled with the greatest possible efficiency.

[0038] In a step S1, the method begins with receiving a predetermined speed and / or torque request for the electric machine 3. In particular, the computer device 6 is specifically designed to execute the method described below or a computer program product executing the method.

[0039] In a step S2, at least one voltage value of an electrical intermediate circuit voltage Ui of the power electronics 2 is estimated with the aid of a mathematical model, preferably based on the equivalent circuit diagram for the mathematical model shown in Figure 3, as a function of the speed and / or torque requirement.

[0040] For this purpose, the mathematical model, as described above, takes into account in particular at least one resistance value of an internal resistance R5 of the battery 4 and a voltage value of an electrical open-circuit voltage Uo of the battery 4. These are determined in particular as a function of a battery temperature and / or an age of the battery 4.

[0041] Furthermore, the mathematical model takes into account in particular at least one power value of an electrical consumption power P3 of an electrical consumer connected to the battery 4, a power value of an electrical drive power of the drive system 1, and / or losses in or between the wiring and the power electronics 2, in particular characterized by a resistance value of a corresponding resistor R4, as described above. In a step S3, at least one current value of an electrical current for one of the phases 5 and / or a rotor of the electrical machine 3 is specified as a function of the speed and / or torque requirement for the electrical machine 3 and the intermediate circuit voltage Ui estimated in step S2. The current value is retrieved in particular from a characteristic map associated with the estimated voltage value of the intermediate circuit voltage Ui.In step S4, the electric machine 3 is finally controlled depending on the specified current value. This concludes the method.

Claims

Claims 1. A method for operating an electric drive system (1), in particular for a motor vehicle, wherein the electric drive system (1) comprises power electronics (2), in particular an electrical voltage converter, an electrical machine (3) that can be controlled by the power electronics (2), and a battery (4) that is or can be electrically connected to the power electronics (2), and wherein the power electronics (2) comprises at least one electrical phase (5) for controlling the electrical machine (3), characterized in that at least one voltage value of an electrical intermediate circuit voltage (Ui) of the power electronics (2) is estimated with the aid of a mathematical model of the drive system (1) as a function of a predetermined speed and / or torque requirement for the electrical machine (3),that at least one current value of an electric current for one of the phases (5) and / or a rotor of the electric machine (3) is predetermined as a function of the speed and / or torque requirement for the electric machine (3) and of the estimated intermediate circuit voltage (Ui), and that the electric machine (3) is controlled as a function of the predetermined current value.

2. Method according to claim 1, characterized in that the mathematical model takes into account a resistance value of an internal resistance (R5) of the battery (4) and / or a voltage value of an electrical open circuit voltage (Uo) of the battery (4).

3. Method according to claim 2, characterized in that the resistance value and / or the voltage value are determined as a function of a battery temperature and / or an age of the battery (4).

4. Method according to one of the preceding claims, characterized in that the mathematical model takes into account a power value of an electrical consumption power (P3) of an electrical consumer connected to the battery (4).

5. Method according to one of the preceding claims, characterized in that the mathematical model takes into account a power value of an electrical drive power of the drive system (1).

6. Method according to one of the preceding claims, characterized in that the current value for the predetermined speed or torque requirement is retrieved from a characteristic diagram associated with the estimated voltage value of the intermediate circuit voltage (Ui), in particular a look-up table.

7. Method according to one of the preceding claims, characterized in that the mathematical model is constructed as an observer, wherein the estimated voltage value for the intermediate circuit voltage (Ui) is compared with a measured voltage value.

8. Computer program product for execution on a computer device (6), characterized in that the computer program product, when used as intended, executes a method according to one of the preceding claims.

9. A data carrier with a computer program product according to claim 8.

10. Electric drive system (1), in particular for a motor vehicle, with power electronics (2), in particular an electrical voltage converter, with an electrical machine (3) that can be controlled by the power electronics (2), and with a battery (4) that is or can be electrically connected to the power electronics (2), wherein the power electronics (2) has at least one electrical phase (5) for controlling the electrical machine (3), characterized by a computer device (6) that is specially designed to execute the computer program product according to claim 8.

11. Motor vehicle, characterized by an electric drive system (1) according to claim 10. 5

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